A professional football player’s body has to be made to take punishment. It’s a violent game, and if a player can’t absorb hits and keep on ticking, there isn’t a place for them in the league.
There is likely no position in which this is truer than running back. They’re tasked to carry the ball forward, either between the tackles or around them, shrugging off hits and would-be tacklers, all while continuously moving forward. And then, when the play is over, and the ball carrier is under a pile of larger men, he gets up, dusts himself off, and does it again.